You're Fired: The Use of Fire to Eliminate Non-Native Plants in a Prairie Restoration

I went on a class field trip to Fernwood Botanic Garden in southwest Michigan when I was in sixth grade. When we toured the restored prairie, the naturalist told us about invasive non-native plants such as garlic mustard and how they destroy native habitats. Most of my class was bored, but I was amazed. I wanted to learn more, especially because my grandfather owns a section of prairie in southwest Michigan. About five years ago, he completed a prairie restoration on some of his land, and I wanted to know if he also had non-native plants growing in his prairie.

Crown vetch (Coronilla varnia), a non-native plant, is one of the biggest problems in restored pairies.

I also learned about prescribed burns as a tool to keep prairies healthy. This was a new concept to me. My father is a firefighter, so I understood fire to be something destructive, not helpful. I began researching both native and non-native plants and the effects of fire on prairie plants. I theorized that in addition to being necessary and beneficial to native prairie plant growth, prairie burns are an excellent tool in the elimination of non-native plant species in prairie restoration plots.

Prairie restorations are an important way to preserve native prairie grasses in Michigan. While Michigan is not usually thought of as a “prairie state,” there were once 100,000 acres of prairie grassland in the state. In southern Michigan, most of the prairie land was turned into farmers’ fields. Today, there are only small prairie remnants and prairie restoration areas.

Purple coneflower (Echinacea pallida) is a common native prairie plant.

Native plants are plants that grow naturally in a specific place. Non-native plants are ones that are brought in from another location. They could be brought in by people or animals. The problem is that many of these non-native plants are aggressive and invasive, meaning that they take right over and push out the native plants. Also, they may not have any natural enemies. Animals and insects may not eat them, so they grow and spread more than native plants. Sometimes non-native plants will choke out all the native plants and completely destroy a native habitat and the food, nesting grounds and cover that animals, birds and insects need.

Prairie grasses and plants are unique. Most of them regrow from the root. Prairie plants have very large root systems. In fact, what you see above ground is only one-third of the total plant. Some roots go down as deep as 20 feet. That is the part that grows back after a fire. Many non-native plants regrow from the part of the plant that is above ground, not from the root.

My theory is connected to prescribed prairie burns. Prairies need fire for several reasons. First, fire cleans out the dead grasses and plants that block the sun and rain from getting to the soil. Second, the ash fertilizes the soil, making it more nutritious. Lastly, some prairie plants need heat to open their seeds.

Because many non-native plants do not regrow from the roots, I wondered if the prescribed prairie burns would destroy them. I would have to test my theory to see if I could prove that fire is an effective way to help rid prairie restoration areas of non-native plants.

I chose three prairie restorations to test. I selected them because two of them were scheduled for prescribed burns and one was not. That one, the Geneva Prairie, would be my “control” prairie. The two scheduled to be burned, the Fernwood Botanic Garden Prairie and the Atkinson Dewey Street Prairie, would be my “test” subjects.

I used metal states and ribbon to mark off my samples.

The first thing I did was to visit each prairie. I did this in the fall before the spring burn. Using metal stakes and ribbon, I staked out six random two-foot-by-two-foot squares and cataloged all the plants in the squares. With the help of some plant identification books and Heidi Gray, the naturalist at Fernwood Botanic Gardens, I identified each of the plants and noted which were native to prairies and which were non-native (Cataloged Prairie Plants). I then figured the percentage of non-native plants in each random sample.

I got to go to the prescribed burn at the Atkinson Dewey Street Prairie. It was really interesting to watch. The land was totally blackened after the fire, but I could see that the fire had really cleared out the underbrush and dead grass. Unfortunately, the Fernwood Prairie fire was on the same day, at nearly the same time, so I couldn’t attend both burns.

Both the Atkinson Dewey Street Prairie and the Fernwood Prairie were burned in early April, so I waited a few months for the plants to grow back. I then repeated the process with each prairie in June and figured out the percentage of non-native plants in each random sample. I returned to each prairie in September to repeat the survey and confirm my results.

I determined that before the prescribed burns, the Atkinson Dewey Street Prairie had approximately 19% non-native plants, the Fernwood Prairie had approximately 20% non-native plants, and the Geneva prairie had 12.83% non-native plants.

In June, more than two months after the prescribed burns, the Atkinson Dewey Street Prairie had approximately 9% non-native plants, the Fernwood Prairie had 18.3% non-native plants, and the Geneva Prairie had 13.2% non-native plants.

From my results, I determined that prescribed prairie burns are an effective tool to help control invasive non-native plants in prairie restoration areas, but fire cannot completely solve the problem. After the prescribed fires, there were still some non-native plant species, although the percentage had decreased. This could be because the fire did not totally destroy the non-native plants, or because a certain number of non-native species also grow back from the root. (This is true of crown vetch, one of the most invasive non-native plants and a big problem for restored prairies in Michigan.) It could also be that the prairie plot was re-contaminated with new non-native plant seeds after the fire. These could have been deposited by the wind, birds or animals, or even on the shoes of people. It also could be that that samples I took before the burn naturally had more non-native plants than the random samples I took after the prescribed burns.

I learned that it is extremely difficult to completely rid a prairie restoration of non-native plants. Only through diligence and a combination of techniques—hand weeding, controlled burns, etc.— is it possible to stop the spread of invasive plants once they become established in an area. The best defense would be to educate the public about non-native plants and to encourage the use of native plants in landscaping so that invasive species are not brought into natural areas. The public should also be educated about the harm that non-native plants can do to an ecosystem.

I plan to continue my field study of all three prairies to determine trends in non-native plant growth. I plan to return to all three prairies this spring, one year after the burns, to sample the non-native plant growth again. It is my hope that by learning more about the behavior of non-native plants, I can determine the best ways to rid prairie restorations of these destructive and invasive plants, thereby making the prairies a healthy natural ecosystem.